1. Field of the Invention
The present invention relates to a clutch-lever manipulation assisting device interposed between a clutch lever and a clutch to add a pushing force of a biasing device to a manipulating force by the clutch lever.
2. Description of Related Art
Conventionally, clutches for motorcycles are constructed such that a crew grasps a clutch lever provided on a steering handle to effect disengagement. A manipulating force at the time of clutch operation is increased corresponding to a magnitude of a transfer torque of a clutch, that is, a magnitude of the output of an engine as mounted. Therefore, motorcycles mounting thereon an engine of high output are in some cases provided with a clutch-lever manipulation assisting device, in which a clutch operation is assisted by, for example, an elastic force of a spring at the time of a clutch operation in the case where the manipulating force is sharply increased.
With a conventional clutch-lever manipulation assisting device a biasing device that assists is coupled to a clutch-side operated lever (operated member) coupled to a clutch lever via a length of clutch wire. The biasing device includes an arm that turns together with the operated lever, and a compression coiled spring with one end thereof coupled to a turning end of the arm, and is constructed such that the operated lever is biased by an elastic force of the compression spring.
The compression coiled spring has the one end coupled to the turning end of the arm and has the other end thereof pivotally supported by a clutch-side support member. That is, in the case where both ends of the compression coiled spring and a turning center of the arm are positioned on a straight line, the elastic force of the compression coiled spring does not act in a direction, in which the arm turns, and the operated lever is not assisted, but the arm turns together with the operated lever upon manipulation of the clutch lever whereby the elastic force of the compression coiled spring is applied to the arm in a direction (a direction, in which the operated lever is turned by an operation of clutch disengagement), in which a turning angle increases. Therefore, the operation of clutch disengagement is performed by a resultant force of a manipulating force, with which the clutch lever is grasped, and the elastic force of the compression coiled spring.
Conventional clutch-lever manipulation assisting devices are constructed such that when an operated lever is turned to a position (referred to below as a clutch-meet position), in which a clutch is fully engaged, in a stroke of clutch engagement, a turning center of the operated lever (the arm described above) and both ends of the compression coiled spring are positioned on a straight line. This is because it is aimed at preventing a force, with which a friction plate of a clutch is pushed, from being decreased by the elastic force of the compression coiled spring when the clutch is in an engaged state.
In a stroke of clutch engagement, the clutch lever is returned to the clutch-meet position, thereafter swings by an amount, in which a so-called play is provided, further in a return direction, and returns to an initial position (referred below to as a return-finish position). At this time, the arm turns by that turning angle, which corresponds to the play of the clutch lever, in a direction of clutch engagement, and the arm is biased in the direction of clutch engagement by the elastic force of the compression of the coiled spring, so that a resultant force of an elastic force of a spring in the clutch and the elastic force of the compression of the coiled spring acts on the clutch lever in a state, in which the clutch lever is positioned in the return-finish position.
Conventional clutch-lever manipulation assisting devices include a biasing device that assists provided midway the length of a clutch wire as shown in FIGS. 12(a)–12(b) and 13(a)–13(c), in addition to one provided at a clutch-side end of the length of the clutch wire as described above.
A conventional clutch-lever manipulation assisting device 1 shown in FIG. 12(a) includes an arm 3 mounted at its turning end to a length of a clutch wire 2, and biasing device 4 coupled pivotally to the turning end of the arm 3. A base end of the arm 3 is pivotally supported by a spindle 5 on, for example, a vehicle frame of a motorcycle. The biasing device 4 includes a first rod 4a connected to the arm 3, a second rod 4b mounted on the includes a first rod 4a to be axially movable, and a compression spring 4c elastically mounted between the first rod 4a and the second rod 4b. A tip end of the second rod 4b is pivotally supported on the vehicle frame, or the like.
The clutch wire 2 is moved leftward in FIG. 12(a) by manipulating a clutch lever (not shown) in a direction, in which a clutch is disengaged. FIG. 12(a) is drawn in a state, in which the clutch lever is manipulated in a direction of clutch disengagement so that a manipulated amount becomes maximum, and the clutch lever is positioned in a so-called draw-finish position. The arm 3 is put in a position indicated by two-dot chain lines A in FIG. 12(a) when the clutch lever is positioned in a return-finish position, and turned to a position indicated by two-dot chain lines B when the clutch lever is positioned in a clutch-meet position. At the time of the clutch-meet position, both ends of the biasing device 4 and a center (spindle 5) of turning of the arm 3 are caused to be positioned on a straight line.
The conventional clutch-lever manipulation assisting device 1 shown in FIG. 12(a) opertates in the same manner as the conventional clutch-lever manipulation assisting device and the arm 3 turns leftward in the figure from a position indicated by B in the figure whereby an elastic force of the compression spring 4c is added to a manipulating force.
Since the biasing device 4 in the clutch-lever manipulation assisting device 1 is coupled to the arm 3 provided midway the clutch wire 2, the clutch lever is manipulated to the draw-finish position from the return-finish position whereby the clutch wire 2 will be pulled a length (output stroke) equal to a length (input stroke) pulled by the clutch lever as shown in FIG. 12(b).
Also, with the clutch-lever manipulation assisting device, a force (necessary input load) required for the clutch lever to effect clutch disengagement varies as shown in FIG. 12(c) corresponding to a manipulated amount (input stroke). In the figure, a clutch reaction force indicates an elastic force of a spring in the clutch, and an assist force indicates an elastic force of the compression spring 4c. Also, a reverse assist force means a force (a resultant force of the elastic force of the spring in the clutch and the elastic force of the compression spring 4c) that biases the clutch lever when the clutch lever is present in the return-finish position.
As shown in FIG. 12(c), a force (necessary input load) required for manipulating the clutch lever is increased at the start of manipulation so as to resist the reverse assist force and gradually decreased until the arm 3 reaches a position (clutch-meet position) indicated by the two-dot chain lines B in FIG. 12(a). After the arm 3 passes the clutch-meet position, the necessary input load is rapidly increased because a clutch reaction force acts on the clutch wire 2. Thereafter, until the clutch lever reaches the draw-finish position, the necessary input load is gradually decreased as the manipulated amount of the clutch lever is increased. Therefore, with the clutch-lever manipulation assisting device 1 shown in FIG. 12(a), a force must be applied twice to an arm that grasps the clutch lever, when the clutch should be disengaged. This phenomenon occurs likewise in the conventional clutch-lever manipulation assisting device.
On the other hand, a clutch-lever manipulation assisting device 6 shown in FIG. 13(a) is not provided with any compression coiled spring for the biasing purpose but constructed in a manner to dispense with a manipulation to moderate a force in the course of disengagement of the clutch. With the clutch-lever manipulation assisting device 6, the length of the clutch wire 9 on a clutch-lever side is coupled to a turning end of an arm 8, one end of which is pivotally supported on a vehicle frame, or the like by means of a spindle 7, and the length of clutch wire 10 on a clutch side is coupled to an intermediate portion of the arm 8. The arm 8 is put in a position indicated by two-dot chain lines A in FIG. 13(a) in a state, in which the clutch lever is positioned in a return-finish position, and put in a position indicated by two-dot chain lines B in FIG. 13(a) at at the time of clutch-meet.
That is, the clutch-lever manipulation assisting device 6 is configured so that a load at the time of a clutch operation is decreased by virtue of a so-called principle of lever. Therefore, with the clutch-lever manipulation assisting device 6, an output stroke amounts to about a half of an input stroke as shown in FIG. 13(b), and a necessary input load amounts to about a half of a clutch reaction force to become substantially constant as shown in FIG. 13(c).
The conventional clutch-lever manipulation assisting device and the clutch-lever manipulation assisting device 1 in FIG. 12(a) involve a problem that a person who performs manipulation is given a sense of incongruity since a necessary input load is once decreased and thereafter gradually increased in a stroke of clutch disengagement. This is because a manipulating force in common clutches for motorcycles is substantially constant when a clutch lever is manipulated from a return-finish position to a clutch-meet position and from the clutch-meet position to a draw-finish position.
Such disadvantage in manipulation can be dissolved by making use of the principle of lever as the clutch-lever manipulation assisting device 6 shown in FIG. 13(a). Since an output stroke amounts to about a half of an input stroke and there is a limit in increasing a manipulated amount of a clutch lever in the construction, however, there is a fear that the clutch cannot be fully disengaged.
The invention has been thought of in order to dissolve such problem, and an advantage of the present invention is to eliminate giving a sense of incongruity to an operator at the time of operating the clutch while adopting a construction, in which the biasing device assists clutch operations and to surely perform disengagement/engagement of a clutch.